Three‐dimensional imaging of chemical phase transformations at the nanoscale with full‐field transmission X‐ray microscopy

The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano‐ and micrometer‐scale factors at the origin of macroscopic behavior. While different electron‐ and X‐ray‐based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X‐ray imaging set‐up is proposed, combining full‐field transmission X‐ray microscopy (TXM) with X‐ray absorption near‐edge structure (XANES) spectroscopy to follow two‐dimensional and three‐dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields.     

X‐ray photon correlation spectroscopy in systems without long‐range order: existence of an intermediate‐field regime

Successful X‐ray photon correlation spectroscopy studies often require that signals be optimized while minimizing power density in the sample to decrease radiation damage and, at free‐electron laser sources, thermal impact. This suggests exploration of scattering outside the Fraunhofer far‐field diffraction limit d²/λR, where d is the incident beam size, λ is the photon wavelength and R is the sample‐to‐detector distance. Here it is shown that, in an intermediate regime d²/λ > Rdξ/λ, where ξ is the structural correlation length in the material, the ensemble averages of the scattered intensity and of the structure factor are equal. Similarly, in the regime d²/λ > Rdξ(τ)/λ, where ξ(τ) is a time‐dependent dynamics length scale of interest, the ensemble‐averaged correlation functions g₁(τ) and g₂(τ) of the scattered electric field are also equal to their values in the far‐field limit. This broadens the parameter space for X‐ray photon correlation spectroscopy experiments, but detectors with smaller pixel size and variable focusing are required to more fully exploit the potential for such studies.     

Mapping the near fields of plasmonic nanoantennas by scattering‐type scanning near‐field optical microscopy

Near‐field optical microscopy techniques provide information on the amplitude and phase of local fields in samples of interest in nanooptics. However, the information on the near field is typically obtained by converting it into propagating far fields where the signal is detected. This is the case, for instance, in polarization‐resolved scattering‐type scanning near‐field optical microscopy (s‐SNOM), where a sharp dielectric tip scatters the local near field off the antenna to the far field. Up to now, basic models have interpreted S‐ and P‐polarized maps obtained in s‐SNOM as directly proportional to the in‐plane ( or ) and out‐of‐plane () near‐field components of the antenna, respectively, at the position of the probing tip. Here, a novel model that includes the multiple‐scattering process of the probing tip and the nanoantenna is developed, with use of the reciprocity theorem of electromagnetism. This novel theoretical framework provides new insights into the interpretation of s‐SNOM near‐field maps: the model reveals that the fields detected by polarization‐resolved interferometric s‐SNOM do not correlate with a single component of the local near field, but rather with a complex combination of the different local near‐field components at each point (, and ). Furthermore, depending on the detection scheme (S‐ or P‐polarization), a different scaling of the scattered fields as a function of the local near‐field enhancement is obtained. The theoretical findings are corroborated by s‐SNOM experiments which map the near field of linear and gap plasmonic antennas. This new interpretation of nanoantenna s‐SNOM maps as a complex‐valued combination of vectorial local near fields is crucial to correctly understand scattering‐type near‐field microscopy measurements as well as to interpret the signals obtained in field‐enhanced spectroscopy.

     

Subdiffraction‐limited chemical imaging of patterned phthalocyanine films using tip‐enhanced near‐field optical microscopy

A tip‐enhanced near‐field optical microscope, based on a shear‐force atomic force microscope with plasmonic tip coupled to an inverted, confocal optical microscope, has been constructed for nanoscale chemical (Raman) imaging of surfaces. The design and validation of the instrument, along with its application to near‐field Raman mapping of patterned organic thin films (coumarin‐6 and Cu(II) phthalocyanine), are described. Lateral resolution of the instrument is estimated at 50 nm (better than λ/10), which is roughly dictated by the size of the plasmonic tip apex. Additional observations, such as the distance scaling of Raman enhancement and the inelastic scattering background generated by the plasmonic tip, are presented. Copyright © 2016 John Wiley & Sons, Ltd.     

Micro‐Raman spectroscopy and VP‐SEM/EDS applied to the identification of mineral particles and fibres in histological sections

Histological sections of a patient affected by an important respiratory disease were analysed firstly by optical microscope(OM)—crossed polarisers—to identify the presence of incorporated inorganic particles, with particular attention to the fibrous ones. Then, the particles/fibres that were found were studied both with micro‐Raman spectroscopy and variable‐pressure scanning electron microscopy with energy‐dispersive spectroscopy (VP‐SEM/EDS). The two techniques allowed the in situ characterisation of the inorganic phases without disintegration of the organic matter. Micro‐Raman spectroscopy was able to identify the vibrating chemical groups of the mineral phase associated with the inorganic grain while the crystalline structure was preserved by the biological system. The VP‐SEM/EDS characterisation, defining the elemental chemical composition of the analysed particle/fibre, allowed confirmation of the mineral phase deducible from spectroscopic data or its identification with certainty when the spectroscopic data were not exhaustive. Copyright © 2009 John Wiley & Sons, Ltd.     

畜禽肉化学成分近红外光谱检测技术研究进展

和传统的肉品化学成分检测方法相比,近红外光谱分析是一种能够快速、简单、安全和可同时测定多种化学成分的肉品检测方法。论述了近年来猪、鸡、牛、羊四种动物肉中粗蛋白质、肌间脂肪、脂肪酸、水分、灰分、肌红蛋白和胶原蛋白七种化学成分的近红外光谱分析检测研究进展,并探讨了目前研究中存在的问题及其原因。从已发表的研究结果可以看出,近红外光谱分析具有替代耗时成本高的现有肉品化学检测方法的巨大潜力,特别是用于商业上同步检测多种化学成分。研究大多采用主成分分析法进行特征光谱筛选,偏最小二乘和修正偏最小二乘法建立校正模型,交互验证进行预测结果评价。目前研究热点集中在肉中脂肪酸含量预测模型和应用近红外高光谱图像和多元回归预测肉中化学成分。近红外光谱预测结果差异性较大,这与样品集选择、光谱预处理和建模方法都有很密切的关系。样品选择对近红外预测精度具有重要的意义,非均质肉样影响了近红外化学成分预测精度。总的来说,肌间脂肪、脂肪酸与水分指标预测效果较好,粗蛋白质和肌红蛋白指标预测效果次之,灰分和胶原蛋白指标预测结果较差。     

Non‐invasive depth profiling by space and time‐resolved Raman spectroscopy

Time‐resolved Raman spectroscopy, spatially offset Raman spectroscopy and time‐resolved spatially offset Raman spectroscopy (TR‐SORS) have proven their capability for the non‐invasive profiling of deep layers of a sample. Recent studies have indicated that TR‐SORS exhibits an enhanced selectivity toward the deep layers of a sample. However, the enhanced depth profiling efficiency of TR‐SORS, in comparison with time‐resolved Raman spectroscopy and spatially offset Raman spectroscopy, is yet to be assessed and explained in accordance to the synergistic effects of spatial and temporal resolutions. This study provides a critical investigation of the depth profiling efficiency of the three deep Raman techniques. The study compares the efficiency of the various deep Raman spectroscopy techniques for the stand‐off detection of explosive precursors hidden in highly fluorescing packaging. The study explains for the first time the synergistic effects of spatial and temporal resolutions in the deep Raman techniques and their impact on the acquired spectral data. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of gamma irradiation on X‐ray absorption and photoelectron spectroscopy of Nd‐doped phosphate glass

X‐ray absorption near‐edge structure (XANES) and X‐ray photoelectron spectroscopy (XPS) of Nd‐doped phosphate glasses have been studied before and after gamma irradiation. The intensity and the location of the white line peak of the L₃‐edge XANES of Nd are found to be dependent on the ratio O/Nd in the glass matrix. Gamma irradiation changes the elemental concentration of atoms in the glass matrix, which affects the peak intensity of the white line due to changes in the covalence of the chemical bonds with Nd atoms in the glass (structural changes). Sharpening of the Nd 3d_5/2 peak profile in XPS spectra indicates a deficiency of oxygen in the glasses after gamma irradiation, which is supported by energy‐dispersive X‐ray spectroscopy measurements. The ratio of non‐bridging oxygen to total oxygen in the glass after gamma radiation has been found to be correlated to the concentration of defects in the glass samples, which are responsible for its radiation resistance as well as for its coloration.     

In situ monitoring of the solution‐mediated polymorphic transformation of glycine: characterization of the polymorphs and observation of the transformation rate using Raman spectroscopy and microscopy

The aim of this work was to investigate the mechanism and progression of the solution‐mediated polymorphic transformation and crystallization of glycine. The identification of the α‐ and γ‐forms of glycine crystals was performed using powder X‐ray diffraction (PXRD), Raman microscopy and in situ probe Raman spectroscopy. The influence of the addition of NaCl and of the process parameters such as saturation temperature, seed size and stirring speed on the transformation behavior from the metastable α‐ form to the stable γ‐ form was examined. In situ probe Raman spectroscopy was used to monitor the solid‐phase properties—polymorphic composition. Fourier transform infrared spectroscopy (FTIR) with a ZnSe window was used to track the liquid‐phase concentration at different times. Besides, the polymorphic transformation of glycine in the solvent was also examined in situ using a microscope with a heating/cooling stage. The integration of the different offline and in situ analytical measurement techniques greatly assisted in accurately and quantitatively perceiving the fundamental phenomena that govern the transformation process. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of self‐repair mechanisms of Phaseolus vulgaris var. saxa using near‐infrared surface‐enhanced Raman spectroscopy

We used surface‐enhanced Raman spectroscopy (SERS) to investigate ultrastructural changes in cell‐wall composition during the self‐repair of lacerated hypocotyls of Phaseolus vulgaris var. saxa. A detailed study of self‐repair mechanisms requires localized information about cell‐wall structure and morphology in addition to the chemical cell‐wall composition. Characteristic Raman and SER spectra yielded two‐dimensional maps of cross sections of P. vulgaris var. saxa visualizing chemical compositions in the walls of different cell types and during various repair phases. SERS substrate particles were produced by the reduction of gold chloride on the plant tissue surface and characterized with absorption spectroscopy, scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. The SERS results were compared with stained cross sections of the same plant using dark‐field microscopy with focus on lignin and suberin contents in repairing cells. In addition, SERS measurements revealed Au cyanide compounds on the cell surface, indicating the formation of hydrogen cyanide during the self‐repair phase. Copyright © 2009 John Wiley & Sons, Ltd.     

Polarized Raman and photoluminescence studies of a sub‐micron sized hexagonal AlGaN crystallite for structural and optical properties

The polarized Raman spectroscopy is capable of giving confirmation regarding the crystalline phase as well as the crystallographic orientation of the sample. In this context, apart from crystallographic X‐ray and electron diffraction tools, polarized Raman spectroscopy and corresponding spectral imaging can be a promising crystallographic tool for determining both crystalline phase and orientation. Sub‐micron sized hexagonal AlGaN crystallites are grown by a simple atmospheric pressure chemical vapor deposition technique using the self catalytic vapor–solid process under N‐rich condition. The crystallites are used for the polarized Raman spectra in different crystalline orientations along with spectral imaging studies. The results obtained from the polarized Raman spectral studies show single crystalline nature of sub‐micron sized hexagonal AlGaN crystallites. Optical properties of the crystallites for different crystalline orientations are also studied using polarized photoluminescence measurements. The influence of internal crystal field to the photoluminescence spectra is proposed to explain the distinctive observation of splitting of emission intensity reported, for the first time, in case of c‐plane oriented single crystalline AlGaN crystallite as compared with that of m‐plane oriented crystallite. Copyright © 2016 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering within silver‐nanoparticle‐decorated nanometric apertures

An analytical approach using enhanced Raman spectroscopy to record molecular vibrations and associated molecular images within nanometric apertures is presented, which can essentially rival or surpass its counterparts, i.e. fluorescence microscopy, by providing unique structure‐specific information forward to chemical identification and structure elucidation. Utilizing a precise nanolithographic technology and the following chemically electroless silver deposition procedure, we deliberately construct the large scale zero‐mode waveguide array in gold film with embossed silver nanostructures on the bottom of nanowells capable of acquiring enhanced Raman spectra with substantial sensitivity and high chemical fidelity. Two chemicals, aminothiophenol (4‐ATP) and Rhodamine 6G, respectively, are employed as molecular indicators to successfully demonstrate the capability of this analytical strategy by exhibiting high‐quality Raman spectra and 2D chemical‐specific images. With a high magnitude objective (60×), we enable to acquire Raman spectra from a single nanometric aperture and quantitatively determine a peak enhancement factor of 3.63 × 10⁵ for ATP, while 1.25 × 10⁶ to Rhodamine 6G, comparable with a regular nanoparticle‐based surface‐enhanced Raman spectroscopy‐active substrate. Overall, the compelling characteristics of this detection scheme highlight its privileges for interrogating the individual molecular behavior in extremely confined geometry and illustrating the chemical insights of trace components without any labeling reagent and extra sample preparation. Copyright © 2013 John Wiley & Sons, Ltd.     

The high‐resolution absorption spectroscopy branch on the VUV beamline DESIRS at SOLEIL

A VUV absorption spectroscopy facility designed for ultra‐high spectral resolution is in operation as a dedicated branch on the DESIRS beamline at Synchrotron SOLEIL. This branch includes a unique VUV Fourier transform spectrometer (FTS) and a dedicated versatile gas sample chamber. The FTS instrument can cover a large UV–VUV spectral range from 4 to 30 eV, with an ultimate line width of 0.08 cm^?1 on a large spectral window, ΔE/E = 7%, over which all spectral features can be acquired in a multiplex way. The performance can be considered to be a middle ground between broadband moderate‐resolution spectrometers based on gratings and ultra‐high‐spectral‐resolution VUV tunable‐laser‐based techniques over very narrow spectral windows. The various available gaseous‐sample‐handling setups, which function over a wide range of pressures and temperatures, and the acquisition methodology are described. A selection of experimental results illustrates the performance and limitations of the FTS‐based facility.     

X‐Treme beamline at SLS: X‐ray magnetic circular and linear dichroism at high field and low temperature

X‐Treme is a soft X‐ray beamline recently built in the Swiss Light Source at the Paul Scherrer Institut in collaboration with École Polytechnique Fédérale de Lausanne. The beamline is dedicated to polarization‐dependent X‐ray absorption spectroscopy at high magnetic fields and low temperature. The source is an elliptically polarizing undulator. The end‐station has a superconducting 7 T–2 T vector magnet, with sample temperature down to 2 K and is equipped with an in situ sample preparation system for surface science. The beamline commissioning measurements, which show a resolving power of 8000 and a maximum flux at the sample of 4.7 × 10¹² photons s^?1, are presented. Scientific examples showing X‐ray magnetic circular and X‐ray magnetic linear dichroism measurements are also presented.     

Subsurface analysis of painted sculptures and plasters using micrometre‐scale spatially offset Raman spectroscopy (micro‐SORS)

A recently developed variant of spatially offset Raman spectroscopy (SORS) for the non‐invasive analysis of thin painted layers, micro‐SORS, has been applied, for the first time, to real objects of Cultural Heritage – namely painted sculptures and plasters. Thin layers of paint originating from multiple restoration processes often applied over many centuries have been analysed non‐destructively using micro‐SORS to depths inaccessible to, or unresolvable into separate layers, by conventional confocal Raman microscopy. The concept has been demonstrated on several artistic artefacts of historical significance originating from Italy and dating from the medieval to the 18th century. The technique extends the depth applicability of Raman spectroscopy and with its inherently high chemical specificity that expands the portfolio of existing non‐destructive analytical tools in Cultural Heritage permitting to avoid cross‐sectional analysis often necessitated with this type of samples with conventional Raman microscopy. Currently, the method is non‐invasive only for artworks that can be placed under Raman microscope although there is a prospect for its use in a mobile system with largely removed restrictions on sample dimensions. © 2015 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons Ltd.     

Phase‐specific Raman analysis of n‐alkane melting by moving‐window two‐dimensional correlation spectroscopy

We use moving‐window two‐dimensional correlation spectroscopy (MW‐2DCOS) for phase‐specific Raman analysis of the n‐alkane (C₂₁H₄₄) during melting from the crystalline solid phase to the intermediate rotator phase and to the amorphous molten phase. In MW‐2DCOS, individual peak‐to‐peak correlation analysis within a small subset of spectra provides both temperature‐resolved and spectrally disentangled Raman assignments conducive to understanding phase‐specific molecular interactions and chain configurations. We demonstrate that autocorrelation MW‐2DCOS can determine the phase transition temperatures with a higher resolving power than commonly used analysis methods including individual peak intensity analysis or principal component analysis. Besides the enhanced temperature resolving power, we demonstrate that asynchronous 2DCOS near the orthorhombic‐to‐rotator transition temperature can spectrally resolve the two overlapping peaks embedded in the Raman CH₂ twisting band in the orthorhombic phase, which had been only predicted but not observed because of thermal broadening near the melting temperature. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.     

Some forensic applications of a combined micro‐Raman and scanning electron microscopy system

The structural chemical analyser (SCA) is a novel accessory that allows the analytical advantages of Raman spectroscopy and scanning electron microscopy with energy dispersive x‐ray detection (SEM/EDX) to be realised in a single hybridised instrument. The combined Raman–SEM/EDX system permits in situ characterisation of a sample based on both its molecular and elemental makeup. This article demonstrates the potential of using the SCA for interrogating trace evidence for criminalistic purposes. Illustrative evidentiary examples (taken from our laboratory's archives) include the examination of a white paint fragment consisting of several layers of the same colour and a sample of explosive mixture recovered from a place of interest. The sensitive SEM imaging contrast mechanisms enabled the optically identical multiple layers of the white paint to be distinguished easily. The individual layers were then unambiguously analysed to establish their elemental profile (from energy dispersive x‐ray (EDX)) and this was cross‐referenced with the chemical information derived from in situ Raman measurements. X‐ray mapping was used as a fast and convenient way of characterising simultaneously multiple solids constituting the explosive mixture. Typical particles were targeted and analysed both by EDX and Raman spectroscopy revealing an unusual chlorate‐based energetic mixture that also contained 2, 4, 6‐trinitrotoluene (TNT) and 2, 4, 6‐trinitrophenylmethylnitramine (Tetryl). Copyright © 2009 John Wiley & Sons, Ltd.     

Near‐room‐temperature photon‐noise‐limited quantum well infrared photodetector

With the modern development of infrared laser sources such as broadly tunable quantum cascade lasers and frequency combs, applications of infrared laser spectroscopy are expected to become widespread. Consequently, convenient infrared detectors are needed, having properties such as fast response, high efficiency, and room‐temperature operation. This work investigated conditions to achieve near‐room‐temperature photon‐noise‐limited performance of quantum well infrared photodetectors (QWIPs), in particular the laser power requirement. Both model simulation and experimental verification were carried out. At 300 K, it is shown that the ideal performance can be reached for typical QWIP designs up to a detection wavelength of 10 µm. At 250 K, which is easily reachable with a thermoelectric Peltier cooler, the ideal performance can be reached up to 12 µm. QWIPs are therefore suitable for detection and sensing applications with devices operating up to or near room temperature.     

An assessment study of tiles from Topkapı Palace Museum with energy‐dispersive X‐ray and Raman spectrometers

A limited number of studies concerning Ottoman ceramic technology have been performed using the scanning electron microscopy‐energy dispersive X‐ray spectrometry and micro‐Raman spectroscopy techniques. The discovery of the ceramics, which were described as ‘Iznik’, at excavation sites outside of the city of Iznik, caused disagreements over the exact origin of Iznik products. In this study, bodies, glazes, and pigments of 46 tile/ceramic shards of unknown origin, which were supplied from the vaults of Topkapı Palace Museum, and two reference tile fragments, known as Kütahya products, supplied from the demolished Surp Krikor Lusavoriç church and, additionally, two Iznik reference tiles were examined using the scanning electron microscopy‐energy dispersive X‐ray spectrometry and micro‐Raman spectroscopy techniques. Results of both techniques were evaluated together for the first time to determine the power of nondestructive Raman spectroscopy technique in differentiation of Ottoman tiles. In this work, bodies of the Kütahya tiles were found to be different than Iznik and Tekfur stone‐paste bodies, which are rich in clay rather than quartz. Two different lead‐alkali glaze compositions were found for Kütahya tiles; one was rich in PbO (over 35%) and the other one was rich in alkali (PbO less than 25%). Barite inclusions were detected in the bodies and in the glazes of some Ottoman tiles, which could be the fingerprint for the Kütahya products. It was found that the under glaze red decoration is essentially a mixture of hematite and quartz in different proportions. Shades of red decoration mainly depend on the amount of hematite in the mixture. Sixteenth century tomato red decoration contains more quartz compared with 17th century dark red decoration. This study showed that a similar technology was also applied at Kütahya in the 16th century. A linear correlation was found between the position of the Raman intense stretching peak Q₃ and lead oxide content of lead‐alkali glazes, which could allow for the differentiation of Ottoman tiles based on the nondestructive Raman analysis. This study provides an important additional reference data and discussion for the Ottoman tiles. Copyright © 2011 John Wiley & Sons, Ltd.